级联拉曼光纤激光器优化设计

【作者】 李发丹；

【导师】 周晓军；

【作者基本信息】 电子科技大学 ， 光学工程， 2007， 硕士

【摘要】 拉曼光纤激光器是一种基于受激拉曼散射效应的光纤激光器,只要具备合适的泵浦源,就能够在很大波长范围内获得激光输出,并可以进行宽带调谐,而且与半导体激光器泵浦光源相比,级联拉曼光纤激光器具有输出功率大与光纤耦合效率高等特点,是拉曼光纤放大器的理想泵浦源。本文对拉曼光纤激光器进行了理论分析,并对表征光纤中受激拉曼散射效应的非线性耦合方程组进行求解,在此基础上对不同类型的级联拉曼光纤激光器进行模拟分析及优化设计,本文的主要研究内容如下:第一,概述了受激拉曼散射的基本原理。分析了级联拉曼光纤激光器的泵浦源,增益介质和谐振腔类型。第二,给出了线型腔多阶级联拉曼光纤激光器的模型。并对表征多阶级联拉曼光纤激光器理论模型的非线性耦合方程组进行了分析。设计了求解方法,用四阶龙格-库塔法结合打靶算法进行求解。由于普通的非线性打靶算法收敛性差,收敛速度慢的特点,给出了多维并行打靶算法。结果表明多维并行打靶算法收敛速度很快,很适合求解这类非线性问题。第三,多维并行打靶算法虽然收敛速度快,但是对于求解多阶拉曼光纤激光器耦合方程,任意设置的各阶Stokes光功率初始值很可能不在收敛域内,导致计算不收敛。本文提出了先用遗传算法对各阶的Stokes光功率初值进行优化筛选,解决了各阶Stokes光功率初值选择的收敛性问题,然后结合并行打靶算法求解。结果表明此方法完全可以解决初值功率的收敛性问题。给出了不同遗传代数下优化筛选的功率计算值的精度问题。第四,在求解的基础上对掺磷拉曼光纤激光器和掺锗拉曼光纤激光器进行了模拟分析,并给出了优化设计参数。更多还原

【Abstract】 Raman fiber lasers (RFL) which base on the stimulated Raman scattering (SRS) in fibers, can generate laser over a wide range of wavelengths once appropriate pump sources are available. RFL can also be tuned in a wide-bandwidth to satisfy practical applications. Compared with laser diodes, as the best pump resources for raman fiber amplifiers ,cascaded Raman fiber lasers(CRFL) are more excellent due to theirs high output power and high coupling efficiency with fibers.This dissertation analyzes characteristics of the RFL numerically. Optimization configurations for different orders of CRFL have been found by solving the nonlinear coupled equations used to describe SRS in the fibers. The main contents of this paper are as following:Firstly, the basic theory of SRS is described and pump resources, gain mediums and types of cavity resonators for the CRFL are introduced.Second, a general structural model and nonlinear coupled equations of multi-order CRFL are presented, and the characteristics of the lasers are also analyzed by solving the coupled equations. The fourth-order Runge-Kutta method in combination with shooting method is put forward to deal with the coupled equations. A multi-dimension parallel shooting method is given to replace the general shooting method because of its better convergence and faster calculating speed. The simulating results demonstrate that the multi-dimension parallel shooting method is very suitable for solving the Raman coupled equations which are the representative of highly nonlinear problems.Third, for the coupled equations of Multi-order Raman fiber laser, the parallel shooting algorithms with faster speed of convergence may also make calculating processes divergent for the reason that the initial values for each Stokes power are all guessed arbitrarily. To overcome this problem, we propose that a method of adopting genetic algorithm (GA) which has great ability to find the optimal values in the global domain is employed to determine the initial values for each Stokes power. Then, the task of find more accurate values is finished by shooting methods since the searching ability of GA is weak in local region. Calculated results show that our scheme can solve the coupled equations effectively without the problem of divergence. The tolerance of our calculated values under the different genetic generation is given.At last, we simulated the characteristics of germanium-doped cascaded Raman fiber laser and phosphorus-doped Raman fiber laser, respectively, based on our proposed method. And the parameters of optimization of cascsded Raman fiber laser are presented.更多还原